1. Field of the Invention
The present invention relates to an image acquisition apparatus, an image acquisition system, and a method of controlling the same. More particularly, the present invention relates to a tomographic image acquisition apparatus that includes an interference optical system for ophthalmologic examination and other similar uses, a tomographic image acquisition system, and a method of controlling the apparatus.
2. Description of the Related Art
A diversity of ophthalmology equipment that utilizes optical equipment is used today. For instance, anterior segment cameras, fundus cameras, confocal scanning laser ophthalmoscopes (SLOs), and various others are used as optical equipment for observation of the eye. Optical coherence tomography apparatus (hereinafter, referred to as OCT apparatus), in particular, are for taking a tomographic image of a sample at a high resolution, and are becoming indispensable ophthalmology equipment for the diagnosis of retinal diseases.
An OCT apparatus uses an interference system that irradiates a sample with low coherence light and combines light reflected from the sample with a reference beam, to thereby acquire a high-sensitive image of the sample. The OCT apparatus is capable of photographing a tomographic image at a high resolution by scanning a sample with low coherence light. The OCT apparatus can therefore photograph a high-resolution tomographic image of the retina of an examined eye at the fundus, and is widely used in retinal diagnosis.
In the OCT apparatus, by executing a scan in a depth direction (direction Z) of the retina, a called A-scan, and by executing a scan a plurality of times in the direction X (B-scan), a tomographic image of the retina called B-scan image is acquired. With the B-scan image, the internal state of the retina can be observed, unlike an image obtained by the conventional fundus camera or the like. Thus, it is possible to effectively observe lesions inside the retina, in particular, macular degeneration and a macular hole.
An apparatus that takes a plurality of images by shifting the B-scan image in the direction Y to thereby obtain a three-dimensional retinal image is being developed. Obtaining the three-dimensional retinal image provides an advantage in observing the extent of a lesion and each layer inside the retina, particularly, in observing the ganglionic layer of optic nerve, which suffers glaucoma.
Japanese Patent Translation Publication No. 2008-508068 discloses an OCT apparatus that shortens the time required to acquire a three-dimensional retinal image by using a plurality of low coherence light beams and acquiring three-dimensional images of a plurality of areas concurrently.
Japanese Patent Application Laid-Open No. 2009-183332 discloses a so-called single-beam OCT apparatus that photographs three-dimensional images of sections of a scanning area, pieces the three-dimensional images together, and presents the resultant image to the user.
The OCT apparatus that acquires separate images concurrently with the use of a plurality of low coherence light beams requires a mechanism for adjusting the optical path length of the reference beam of each low coherence light beam in order to obtain the optimum image quality for each low coherence light beam. Adjusting the optical path length for each low coherence light beam means that a tomographic image of a different depth is photographed with each low coherence light beam.
Because tomographic images photographed with the respective low coherence light beams are photographs of different depths, users find it difficult to understand the positional relation between the tomographic images that are displayed side by side as they are.
The adjustment of three-dimensional image display positions disclosed in Japanese Patent Application Laid-Open No. 2009-183332 utilizes the similarity between three-dimensional images to be pieced together around the edges. The positioning accordingly takes time.